Understanding the pathogenesis of cell cycle diseases (e.g., cancer) is complex due to the multiplicity of protein-protein interactions that must be considered. The view of protein-protein interactions as highly inter-connected networks embraces this complexity at the outset, and holds out the promise for the discovery of new therapeutic targets and strategies. To realize this promise, we must understand how key network proteins - modular signaling proteins - drive cellular signal transduction. Mounting evidence shows that these proteins have significant conformational dynamics that change upon target binding. This suggests a functional link between network signaling and protein motion. Yet, most analyses of protein interaction networks implicitly assume static structures. Hence, defining the influence of conformational dynamics on signaling within protein-protein interaction networks remains an outstanding challenge in biology. The goal of our proposed research is to deepen our understanding of how the functional motions of modular signaling proteins affects normal versus pathogenic network signaling, and eventually suggest new strategies for the design of ligands targeting dynamic modular proteins. Toward this goal, we explore two hypotheses developed from our recent work: (1) modular signaling proteins vary the sequences of their recognition loops to enhance binding preference;this has implications for interaction diversity and signal routing within the network;(2) modular signaling proteins use inter-domain interactions to stimulate changes in dynamics that allosterically modulate catalytic activity;this has implications for the mechanisms by which individual proteins process chemical signals. To investigate these hypotheses, we propose NMR investigations of dynamics-activity relationships in a model protein, human Pin1. Pin1 is a mitotic regulator consisting of a docking module (WW domain) flexibly linked to a catalytic module (isomerase domain), and is a current cancer target. Its robust biochemical properties make it an excellent model system for exploring fundamental properties of modular proteins. Investigations will use full-length Pin1, its isolated domains, and known Pin1 substrates/inhibitors. PUBLIC HEALTH RELEVANCE This proposal describes studies of a model system to understand how intrinsic protein dynamics enable biological networks to maintain cell survival and growth. The proposed research will provide new insights into the molecular origins of disease.